A coil arrangement that can be employed as a power transformer in a switch mode power supply is described, for example, in U.S. Pat. No. 5,543,773. The coil arrangement revealed in this document uses a primary and a secondary winding which are mounted onto a trapezoid core and interleaved on the same winding layer. The aim of this arrangement is to minimize the leakage flux density and thus to minimize losses of the coil arrangement, and, more generally, to minimize winding conduction losses. To this effect, a relatively complex, interleaved winding procedure is provided.
Due to the rapid development in power electronics, particularly in the field of switch mode power supply technology, inductive components have gained significantly in importance. The tendency towards higher integration densities, which was extremely successful in the case of semiconductor components, is also in demand for magnetic components. A reduction in the size of magnetic components can be particularly achieved by increasing the working frequency (high-frequency coils for power applications are currently being produced in a range of between 100 kHz and a few MHz). The demand for a higher working frequency and high efficiency has produced winding structures or coil arrangements that show the least possible skin or proximity effect (please see: IEEE Proceedings ICIT03: R. Weger, “Resonant Converter with Current Controlled Inductances”, 2003, Maribor, Slovenia).
Conventional magnetic components consist of a core that conducts the magnetic flux (typically a ferrite material in the case of high-frequency applications), and a core body that carries one or more windings. The general aim is to make the core small enough so that its winding window will be as full as possible. The resulting multi-layer windings, however, create considerable losses through skin effect or proximity effect.
A known approach in the design of more compact inductive components, in particular flatter and more easily fabricated components, is pursued using planar technology. Inherent to this technology, however, are winding geometries whose magnetic fields have an impact well beyond the immediate vicinity of the component. This detrimental characteristic is particularly evident in the case of magnetic components that have low relative effective magnetic permeability (e.g. storage coils) and results in undesirable induction effects on adjoining circuit components and in additional power dissipation. The object of the invention is to provide a coil arrangement which is suitable for use as a high-frequency choke, particularly as a storage choke, and also for use in high-frequency transformers as found, for example, in switch mode power supplies. The coil arrangement according to the invention is designed to eliminate the shortcomings of the prior art as described above. The object of the invention is to produce flatter, more compact and more efficient magnetic components. The coil arrangement should have good power density, high efficiency and excellent characteristics in terms of electromagnetic compatibility (EMC) and electromagnetic noise emission.